What is a hypernova?

A hypernova is a theoretical type of supernova produced when exceptionally large stars collapse at the end of their lifespan. In a hypernova, the core of the star collapses directly into a black hole and two extremely energetic jets of plasma are emitted from its rotational poles at nearly light speed. These jets emit intense gamma rays, and are a candidate explanation for gamma ray bursts. - Wikipedia

What causes hypernovae?

When a white dwarf reaches the Chandrasekhar limit, the maximum mass it can get, it collapses into a neutron star or a black hole. During this breakdown the remaining carbon and oxygen atoms go through fusion, creating a shockwave. Once that liberated energy reaches the surface of the star, its luminosity increases significantly and the outer layers are blown apart. This explosion is called a supernova. These stellar detonations are so impressive that an observer would notice a significant increase in the star's luminosity millions of light years away. This process is similar, yet much more violent, than that of novae. A nova is when the white dwarf doesn't reach the Chandrasekhar limit, but incites nuclear fusion in the matter it has accreted on its surface.

A hypernova is the explosive result of a super massive star's core collapsing directly into a black hole. When the collapse occurs unshackled energy is freed at high frequencies, releasing two extremely energetic jets of plasma emitting from its rotational poles at nearly light speed. These jets of plasma emit gamma rays. Eta Carinae is a prime candidate for a hypernova. Probably being the most massive star in the galaxy it tips the scale at 100-120 times the mass of our sun and is believed to burn between 20,000° and 50,000° Fahrenheit. Comparatively, our sun gets up to around 10,000° Fahrenheit. Because of its mass and temperature Eta Carinae will live a relatively short life, perhaps 25,000 years compared to a standard star's 10 billion years. Eta Carinae is between 7,000-8,000 light years away from Earth and when it finally blows we'll know it.

* The changing intensity of a gamma-ray burst. On the left is an image of the gamma ray sky showing the burst becoming the brightest object. On the right is a plot of the changing brightness with time. The first gamma-ray burst was seen in the year 1967 (although it was not reported to the world until 1973) by satellite-borne detectors intended to look for violations of the Nuclear Test Ban Treaty. Credit: BATSE *

What would happen if a hypernova occurred near Earth?

If a hypernova were to occur within 3,000 light years from Earth it could easily wipe out all life on the planet, even bacteria. If the Earth were within the path of one of the energetic cones the interactions of the gamma rays in the upper atmosphere would produce a lethal dose of highly penetrating ionized particles, destroying life on the surface, underground and underwater. The initial bombardment would immediately destroy the ozone layer and detonate the atmosphere akin to that of the simultaneous discharging, at the bare minimum, of one-kiloton of TNT per km^2, over the whole hemisphere facing the phenomenon. Ionization, the separation of atoms via gaining energy and losing electrons, would take place converting the oxygen and nitrogen in the atmosphere into nitrogen dioxide. Before covering the Earth in a black cloud comparable to that of urban smog, the sky would burst into flames and fireballs, creating global storms of acid rain and possibly fire. However, before all of the previous occurred, the actual radiation would hit the surface. The radiation energy level would be roughly around 10^4 to 10^7 eV (electron volts). If compared to a standard medical x-ray machine's 200,000 eV (and needing a protective lead vest), you get up to 1 million times the radiation! Radiation affects high atomic-number elements more. The most abundant high atomic-number elements in biological organisms are calcium and potassium. These two elements are utilized in muscle function, and ionizing radiation would cause extreme cramping of muscles, making a rather stiff and painful, but quick death.

After the initial impact killed most surface organisms, the brief absence of the ozone layer would allow the sun's ultraviolet rays to barrage the Earth, reaching the depths of the oceans. Water and mud create a buffer-zone for ionized radiation, so most amphibious eggs and aquatic life would survive the hypernova's radiation. However, ultraviolet radiation can penetrate tens of meters of water, so it could harm marine organisms at these depths. Once the gamma ray and ultraviolet ray attack is over, nuclear winter would begin due to the nitrogen dioxide flavored atmosphere smothering the Earth and shielding her from the sun's warming light. These same effects have been conjectured to cause the most devastating mass extinction in our planet's history around 440 million years ago.

How often to hypernovae occur?

The rough estimate is every 200 million years. That would mean the Earth is past due by 260 million years. How could we be so overdue? It's fairly simple, actually. If hypernovae only occur in massive stellar objects at least 40 times the mass of our sun, then we're completely safe. The closest object is Eta Carinae some 7,500 light years away. Take into account its distance and the only thing that would happen if Eta Carinae went hypernova is that Earth-bound observers would see the increase in luminosity and satellites in the southern hemisphere would be fried. The Earth may be overdue by a few hundred million years, but our planets has survived possibly several in its 4.5 billion year lifespan and now there are none left in the neighborhood to bully us.